725 



to Diatoms after which he could ascertain that it was certainly mud 

 from Rockanje and that from a layer agreeing with samples 4 to 6 

 from the deep boring. Tlius the B'ango of Battaglia was investigated 

 and it appeared that this is also recognisable by a definite kind of 

 Diatoms. The Diatoms as "characteristic fossils" could again be of 

 use here. When, therefore, tlie strong radio-activity of the mentioned 

 sample had also appeared in my case, we passed on to a second 

 enlarged investigation with the purpose of obtaining yet closer 

 indications about the question that concerns ns here. This research 

 contains the second series of experiments arranged higher up under 

 Part II (Cf. also Introduction). 



Part II. 



Description of the method of inquiry, viz. -. the ''direct method". 

 This is principally to the effect that a part of the dried mud is 

 weighed and placed into the ionisation-space; the radio-active sub- 

 stances, so 'not only the emanations present in it, cause ionisation 

 of the air, which is again measured. Tliis method, introduced already 

 by Elster and Geitel for definitions of the radio-activity of rock and 

 soils arid at present still used for these, among others by Prof. Gockel 

 in Freiburg, has, however, been disputed on various grounds^) and 

 it unquestionably has considerable drawbacks as a measuring method ; 

 among others this, that when applied as above mentioned it is not possible 

 to obtain an absolute definition or mutual comparison of the quantity 

 of radium, nay a mutual comparison of the activity as a whole 

 cannot even strictly be carried out. For the ionisation may be the 

 consequence of radium and its radio-active products, but at the same 

 time of thorium and other active substances, the rays of which 

 ionise in a very unequal degree. Then, the absorption of the rays 

 is also disturbing, because it gives differences, for the various substances 

 as well as for the divers radiations. Overagainst this we may, 

 however, mention as a very important advantage of the "direct 

 method", that we can get on with it so much quicker; no protracted 

 chemical operations are required as in the case of the emanation 

 method; with the electric measurement we need not await the 

 formation of the equilibrium of the substance employed with the 

 radio-active products to be formed by it. Thus the measurement 

 will only take Prof. Gockel an hour, without mentioning the preceding, 

 necessary determination of the natural ionisation. Witli the use of 

 a sensitive electrometer, however, this advantage is shown more 

 favourably yet. Thus it was possible for me to examine 40 samples 



1) Qf. K. H. BücHNER. Jahibuch Rad. u. El. 1913. 



52 

 Proceedings Royal Acad. Amsterdam. Vol. XX. 



